This invention relates to techniques for introducing phase shifts in RF applications, and more particularly to phase shifting techniques using micro-electro-mechanical switches (xe2x80x9cMEMSxe2x80x9d).
Exemplary applications for this invention include space-based radar systems, situational awareness radars, and weather radars. Space based radar systems will use electronically scan antennas (ESAs) including hundreds of thousands of radiating elements. For each radiating element, there is a phase shifter, e.g. 3 to 5 bits, that, collectively in an array, control the direction of the antenna beam and its sidelobe properties. For ESAs using hundreds of thousands of phase shifters, these circuits must be low cost, be extremely light weight (including package and installation), consume little if no DC power and have low RF losses (say, less than 1 dB). For space sensor applications (radar and communications) these requirements exceed what is provided by known state of the art devices.
Current state of the art devices used for RF phase shifter applications include ferrites, PIN diodes and FET switch devices. These devices are relatively heavier, consume more DC power and more expensive than devices fabricated in accordance with the present invention. The implementation of PIN diodes and FET switches into RF phase shifter circuits is further complicated by the need of additional DC bias circuitry along the RF path. The DC biasing circuit needed by PIN diodes and FET switches limits the phase shifter frequency performance and increase RF losses. Populating the entire ESA with presently available T/R modules is prohibited by cost and power consumption. In short, the weight cost and performance of the currently available devices fall short of what is needed for ESAs requiring electrically large apertures and/or large numbers of radiating elements, e.g. greater than 5000 elements.
Other applications for the invention include switchable attenuators, switchable filter banks, switchable time delay lines, switch matrices and transmit/receive RF switches.
In accordance with one aspect of the invention, an electronically scanned array is described. The array includes a linear array of radiating elements, with an array of phase shifters coupled to the radiating elements. An RF manifold including a plurality of phase shifter ports is respectively coupled to a corresponding phase shifter RF port and an RF port. A beam steering controller provides phase shift control signals to the phase shifters to control the phase shift setting of the array of the phase shifters. The phase shifters each include a plurality micro-electro-mechanical (xe2x80x9cMEMxe2x80x9d) switches responsive to the control signals to select one of a discrete number of phase shift settings for the respective phase shifter.
In accordance with another aspect of the invention, an RF phase shifter circuit includes first and second RF ports, and a switch circuit comprising a plurality of micro-electro-mechanical (xe2x80x9cMEMxe2x80x9d) switches responsive to control signals, said switch circuit arranged to select one of a plurality of discrete phase shift values introduced by the phase shifter circuit to RF signals passed between the first and second RF ports, the circuits connected to provide a single-pole-multiple-throw (SPMT) or multiple-pole-multiple-throw (MPMT) switch function.